Squashed merge commit uses garbage commit message instead of MR title

Summary

Whereas an MR used to use the MR title as the commit message, it now by default picks the longest commit message from the merged branch. However when using the fast-forward merge option, there is no way to edit the commit message and no indication that the behavior has changed leading to highly unexpected behavior for our users.

The result in any instance where the feature branch has had to first resolve any merge conflicts from master, is that the new merge commit is a garbage message from the feature branch and no indication of what has actually been merged.

This has completely broken our workflow because we can no longer do a squashed fast-forward merge request without trashing our git history.

Steps to reproduce

Create a project with fast-forward merge requests enabled

Create some commits on master

Create a feature branch and add commits that will create a conflict

Merge master into the feature branch, resolving the conflicts

Create a merge request to merge feature branch into master (no option to change the message is given)

Perform the merge request and enable the squash option

The new commit on master will be the text of the conflict resolution from step 4